A conventional RFID tag typically comprises an integrated circuit transceiver capable of transmitting a unique serial number or other identifying information to a nearby reader in response to a query from the reader. Many RFID tags are “passive” in that they do not include a battery or other power source, but instead obtain the power necessary to operate from the query signal itself. RFID tags are expected to replace printed barcodes in consumer product applications. Also, ongoing RFID tag development efforts have led to significant cost and size reductions, which should result in a rapid proliferation of RFID tags into many new areas of use. For example, proposals have recently been made to integrate RFID tags into currency.
The impending ubiquity of RFID tags, however, also poses a potentially widespread threat to consumer privacy. The simplest RFID tag will broadcast its unique identifying information to any nearby reader. An example of an inexpensive RFID tag providing such basic functionality is described in S. E. Sarma, “Towards the five-cent tag,” Technical Report MIT-AUTOID-WH-006, MIT Auto ID Center, 2001. This RFID tag transmits a static, 64-to-128-bit identifier on receiving a reader query. The movements of a given consumer or other user can therefore be readily tracked by simply monitoring the RFID tags in goods carried by or otherwise associated with that user.
The above-cited U.S. patent application Ser. No. 10/673,540 discloses techniques for selective blocking of RFID tags in an RFID system, so as to provide protection of consumer privacy. In an illustrative embodiment, a “blocker” tag interferes with a singulation protocol that a reader uses to communicate individually with other RFID tags. While inexpensive to manufacture in quantity, blocker tags are nonetheless special-purpose devices, and thus introduce a level of complexity that may pose an obstacle to their deployment.
Accordingly, a need exists for a system that offers somewhat weaker privacy protection than complete blocking, but with the benefits of greater privacy policy flexibility and minimal alteration to standard tags or readers.